1. Field of the Invention
The present invention relates to a liquid suspension composition having a novel form of gallium particles suspended in a solvent. The present invention also relates to a process for producing said composition and uses thereof.
2. Background Information
Covering the surface of metal particles such as copper, zinc, lead, iron and MoS.sub.2 with coating agents is one of the well known techniques of modifying the properties of metals. It is also known that such coated fine metallic particles can be formulated in pastes, used as lubricants or find various other uses. Japanese Patent Public Disclosure No. 58-125796 entitled "Solid Lubricant" shows a solid lubricant comprising wax and at least one additive selected from the group consisting of molybdenum disulfide, tungsten disulfide, boron nitride and graphite. The present inventors previously filed a patent application entitled "Ski Wax" (later published under Japanese Patent Publication No. 62-8460) which proposes that a lubricant composition containing metallic gallium either independently or alloyed with at least one metal selected from the group consisting of In, Zn, Sn, Al, etc. be used as a ski wax. Commercially available ski waxes include all-purpose waxes (commonly referred to as "silver paraffin wax") and waxes for competition, and they are all based on paraffin wax. Another use of metallic gallium is as a solid lubricant as disclosed in U.S. Pat. Nos. 3,405,063 and 3,391,080.
As shown above, all of the conventional uses of gallium or gallium alloys are based on gallium in the metallic state. The melting point of gallium is extremely low (29.78.degree. C.) and unlike other metals, it cannot be reduced to particles at elevated temperatures, so the scope of applications in which it can be used has been very limited.
The present inventors successfully established a technique by which metallic gallium or gallium alloy that was previously held difficult to reduce to a particulate form could be processed to fine particles not larger than 150 .mu.m (microns), and even to finer particles not larger than 50 .mu.m (microns). With a view to finding some use of these fine gallium particles, the present inventors conducted extensive studies on a method of using them in suspension. However, in all cases attempted, gallium particles simply settled on the bottom of liquid media instead of being suspended therein.
In order to overcome this problem, the present inventors continued their efforts and finally found that metallic gallium particles which would otherwise simply settle on the bottom of suspension media could successfully be suspended in the media when the surface of particles of a size not greater than 150 .mu.m (microns) or even finer particles of a size of 50 .mu.m (microns) and below was covered with a certain kind of coating agent. The present invention has been accomplished on the basis of this finding.
The process for producing fine metallic gallium or gallium alloy particles which can be used in the present invention is disclosed in the co-pending Japanese Patent Application No. 1-104996/1989, mentioned above.
The process comprises the steps of melting metallic gallium or gallium alloy in an atmosphere of inert gas such as nitrogen or argon at a temperature higher than the melting point of gallium or gallium alloy to be melted, but not higher than 100.degree. C., preferably at a temperature in the range of 70.degree.-90.degree. C. and atomizing the molten metal through a nozzle into a cooling medium which can be a plain water or an aqueous solution of at least one compound selected from the group consisting of alcohols, oleic acid and salts thereof, such as sodium oleate and coating agents such as a surfactant, keeping the cooling medium at a temperature not higher than 10.degree. C., preferably not higher than 5.degree. C., said cooling medium being placed in open air or in a sealed tank which is kept under an inert gas atmosphere. The pressure of inert gas for atomizing the molten metal from the nozzle is preferably in the region of 5-10 kg/cm.sup.2 when nitrogen is used for that purpose. Proper inert gas pressure can be determined depending on the desired particle size of the product fine particles. More detailed information can be found in the co-pending Japanese Patent Application No. 1-104996, mentioned above.